Aluminum is widely used for interconnects in semiconductor devices. However, aluminum has been found to be susceptible to a number of problems that may lead to device failure. Component densities (number of components per substrate area within an integrated circuit) typically are becoming higher as the size of components within a semiconductor device become smaller. The higher component density typically causes higher current densities in conductive layers when the device is operating. The higher current density generally results in an increase of device failure because of electromigration, which is a current-induced mass transport that is a function of current density and temperature of the device. Pure aluminum has problems with electromigration. In addition to electromigration, corrosion of the aluminum is a problem and is usually caused by chlorine exposure to the aluminum in an ambient including water, such as air exposure of an aluminum layer immediate following a dry etching step using chlorine-containing chemistry.
In an attempt to solve the problems discussed above, an element, such as silicon (Si), copper (Cu), nickel (Ni), or chromium (Cr) has been added to aluminum to form alloys. In reality, these alloys either do not solve all of the problems previously discussed or cause other problems. Electromigration is typically measured in terms of median-time-to-fail (MTTF) for a given current density and temperature. At a current density of about 4.times.10.sup.6 amperes per square centimeter and a temperature of about 175 degrees Celsius, the MTTF for Al-Cr is reported to be about 830 hours and that of Al-Ni is reported to be only about 300 hours.
In addition, many aluminum alloys do not etch similar to aluminum and require aggressive processing conditions that may attack other portions of the semiconductor device, such as silicon dioxide. Therefore, new process steps may need to be developed. Also, when the concentrations of some of the elements in the aluminum alloy become too high, the resistance of the conductive layer may be too high.